auto start are simply as... i have them for both my cars..
pros? great in summer when the weather is hot; great for winter when you need to warm up the car when u wanna save some time sitting inside.. waiting..
cons? yes, you actually downgrade your alarm system, simply bcoz u gotta put the chip thingy near the ignition.. which bla and bla (not gonna explain much in detail) equals poor protection for your car. Yes, that is when insurance is important for u, coz when stolen ... ... ... (fill in da blank)
cost for alarm system with autostart these days cost around $100-$200. installation another $270-500 depending on how much they wanna charge u for it..
Worth it or not? It depends on what u want.. If i fuking wan a turbo and u giv me a supercharger, i feel sad, but u might be happy with te supercharger~ (stupid explaination )